What causes input offset voltage in op-amps and how is it compensated?

Input offset voltage (Vos) results from mismatches in the differential input stage transistors, including threshold voltage differences, geometry variations, and temperature gradients. Compensation methods include: Internal nulling using offset trim pins with external potentiometer, Auto-zero techniques (chopper stabilization, correlated double sampling) achieving sub-microvolt offsets, External circuit compensation using offset adjustment resistors, and Selecting precision op-amps with laser-trimmed inputs. For high-precision applications, also consider offset drift with temperature (typically 1-10 uV/C).